In the development, completion, and operation of natural hydrocarbon reservoirs, various setting systems are in use.
These systems are used for sealing or cementing the region between metal casing and the formation wall. Other applications include the hydraulic isolation of abandoned or productive zones as described for example in the published International patent application WO-9500739.
The known setting systems are based on either cementitious materials, e.g. cements, particularly Portland cements, blast furnace slag, fly ash/lime mixes and mixtures of these materials, on other ceramic-forming materials, or on polymer materials, such as thermosetting polymers.
Cement-based setting compositions are known for example from U.S Pat. Nos. 4,721,160 and 5,258,072. In some of the known compositions a styrene/butadiene latex is added to the cement in order to impart certain desirable properties, such as fluid loss control, to the composition.
A rubber latex based composition for use in completion or remedial operations in subterranean formations or wellbores is described in the U.S. Pat. No. 5,159,980. The disclosed compositions are comprised of an aqueous dispersion of rubber, a vulcanizing agent and a vulcanization activator. A solid rubber plug or seal is formed therefrom by allowing the compound to vulcanize. The known composition is not thixotropic and therefore not applicable for important operations in horizontal wells.
U.S. Pat. No. 4,649,998 describes a rubber based emulsion for consolidating sand particles. The emulsion also contains an ester which by hydrolysation reduces the pH of the emulsion and thus causes the nitrile rubber to coat the sand grains. The known emulsion is highly specifically designed for sand consolidation and has little use in many other remedial operations, e.g. for plugging formation and the like.
In view of the ever increasing demand for improved well completion and remedial operation techniques, it is an object of the present invention to provide a latex-based setting composition which can be adjusted to a broad range of setting times.
Another object of the present invention is to provide a setting system for wellbore application with improved pumpability. Various well completion and remedial operation require the setting system to be pumpable through small holes, gravel packers, or slotted liners. In particular for coiled tubing, where the diameter of the drill string is small compared to conventional drill strings, the known compositions often suffer a significant frictional pressure drop.